Technical Abstract:
Landscape redistribution of soil carbon is common within agricultural ecosystems, and associated riparian wetlands are often impacted by sedimentation with upland soils. Little is known about the effects of upland sediment deposition on carbon dynamics within riparian wetlands. To assess sedimentation impact, we obtained intact profile samples of wetland soil and used the combination of 210Pb and 14C chronological markers to determine rates of carbon and mineral deposition over the complete history of a wetland within a first-order catchment under agricultural management. We have characterized the wetland soil as having substantial post settlement deposition as evidenced in places by a substantial layer of mineral soil that buried the original histosol. More generally, the intact soil cores contained a local soil carbon minimum within the top 20 cm of the profile which is characteristic of a recent period of rapid upland soil deposition. Radiocarbon dating showed that the soil C above the minimum was recently sequestered (modern C). The magnitude of the modern C pools within these profiles provides strong evidence for accelerated C sequestration associated with rapid mineral deposition. The 210Pb chronological data will be discussed.